VMS Help MACRO, VAX MACRO Assembler, Directives, .IF FALSE (.IFF)  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Starts a  subconditional  assembly  block  to  be  assembled  if
    the condition  test  specified  when  the  conditional assembly
    block was entered was false.  The subconditional  assembly  block
    that  starts with  .IF_FALSE  continues  up  to  the  next
    subconditional assembly directive or to the end of the conditional
    assembly block.

      .IF_FALSE

    The alternate form of .IF_FALSE is .IFF.